Trailer backup aid speed limiting via braking

Abstract

A trailer backup assist system for a vehicle reversing a trailer includes a brake system and a throttle sensor module outputting a throttle application signal. The system further includes a control module estimating a road grade beneath the trailer and outputting a brake torque request to the brake system based on the estimated road grade and the throttle application signal.

We claim: 
     
       1. A trailer backup assist system for a vehicle reversing a trailer coupled therewith, comprising:
 a vehicle brake system; 
 a vehicle sensor system outputting a detected vehicle speed; 
 a vehicle throttle system including a sensor outputting a throttle application signal; and 
 a controller implementing a backup mode including:
 determining an initial brake torque demand based on an error between the detected vehicle speed and a threshold vehicle speed; and 
 calculating an estimated grade of a surface on which the trailer is positioned and adjusting the initial brake torque demand based on the estimated grade and the throttle application signal to derive a modified brake torque demand that is output to the brake system. 
 
 
     
     
       2. The trailer backup assist system of  claim 1 , wherein the initial brake torque demand is predetermined to maintain the trailer outside a jackknife condition with respect to the vehicle. 
     
     
       3. The trailer backup assist system of  claim 1 , wherein the controller includes a proportional-integral-derivative controller that outputs the initial brake torque demand. 
     
     
       4. The trailer backup assist system of  claim 3 , wherein the controller derives the modified brake torque demand by feeding forward respective values based on the estimated grade and the throttle application signal to the initial brake torque demand. 
     
     
       5. A method for assisting a vehicle reversing a trailer, comprising:
 detecting a vehicle speed; 
 determining when a road grade estimate is available; receiving a throttle application signal from a vehicle throttle and 
 implementing a backup mode including:
 determining a brake torque request based on a difference between the detected vehicle speed and a target speed, the target speed being initially set to a predetermined backing threshold speed; 
 outputting the brake torque request to a vehicle brake system; 
 detecting an overspeed condition relative to a predetermined backing condition; 
 adjusting the target speed to below the predetermined backing threshold speed to increase the brake torque request in response to the overspeed condition; and 
 calculating an estimated grade of a surface on which the trailer is positioned and adjusting the brake torque request based on the estimated grade and the throttle application signal to derive a modified brake torque request that is output to the brake system. 
 
 
     
     
       6. The method of  claim 5 , wherein outputting the brake torque request is carried out using a proportional-integral-derivative controller based on tithe difference between the detected vehicle speed and the target speed. 
     
     
       7. The method of  claim 6 , wherein:
 the overspeed condition is the vehicle speed being above the predetermined backing threshold plus a maximum error. 
 
     
     
       8. The method of  claim 6 , wherein:
 the overspeed condition is a determination that the vehicle speed is in excess of the predetermined backing threshold speed for a predetermined time interval. 
 
     
     
       9. The method of  claim 5 , further including:
 returning the target speed to the predetermined backing threshold speed in response to a detection that the vehicle speed has been lowered to below the predetermined backing threshold speed. 
 
     
     
       10. A trailer backup assist system for a vehicle reversing a trailer, comprising:
 a vehicle brake system; 
 a speed detector; 
 a throttle sensor module outputting a throttle application signal; and 
 a controller:
 receiving a detected speed from the speed detector, determining a brake torque request based on a difference between the detected speed and a target speed, the target speed being initially set to a predetermined backing threshold speed, and outputting the brake torque request to the vehicle brake system; 
 lowering the target speed upon one of the detected speed being in excess of the predetermined backing threshold speed for a predetermined time interval or the detected speed being in excess of the predetermined backing threshold speed plus a maximum error; 
 implementing a road grade estimation routine with respect to a surface on which the trailer is positioned; and 
 when a road grade estimate is available, providing a feed-forward adjustment to the brake torque request based on the road grade estimate and the throttle application signal, before lowering the target speed, to maintain the speed of the vehicle below the predetermined backing threshold speed. 
 
 
     
     
       11. The trailer backup assist system of  claim 10 , wherein the controller includes a proportional-integral-derivative controller that receives as input the difference between the detected speed and the target speed. 
     
     
       12. The trailer backup assist system of  claim 10 , wherein:
 the controller outputs the brake torque request to the brake system to maintain the speed of the vehicle below the predetermined backing threshold speed. 
 
     
     
       13. The trailer backup assist system of  claim 10 , wherein the controller raises the target speed in response to detecting that the vehicle speed has been lowered to below the predetermined backing threshold speed. 
     
     
       14. The trailer backup assist system of  claim 10 , wherein the controller further raises the target speed at a controlled rate.